low carbon energy and engineering

end of domestic-scale chp?

It was announced this month that BG Microgen are closing their doors. Microgen is one of two major players in the much hyped and still nascent domestic-scale CHP market. Why would a company backed by British Gas, with over £50m already invested, and poised to take a significant share of a huge market (so we’re told) close their doors just like that?

The term micro CHP applies to any combined heat and power plant under 50 kWe but in this case we’re talking about tiny domestic-scale units (around 1kW electrical and 8kW thermal) fuelled by gas and aimed at replacing domestic boilers. They are remarkable because they generate electricity using a stirling engine and use the resulting heat for space and water heating in the home.

In the right conditions, these units can reduce carbon emissions because they’re much more efficient at making use of fuel than a typical UK power station. In most large centralised power generation, less than 40% of the input fuel energy ends up as usable electricity and the rest is lost up the cooling tower as waste heat. Micro CHP, on the other hand, can be up to 90% efficient.

Micro CHP has rocketed onto the scene in the last few years, with dramatic promises of reducing CO2 emissions from UK homes. Suddenly micro CHP was everywhere. It featured heavily in the energy white paper. The DTI Microgeneration Strategy predicted that by 2050, 30 – 40% of the UK’s electricity demand could be met with mircogeneration with micro CHP “leading the way”. It also stated that micro CHP was economically viable under all the economic scenarios considered by the EST in their study into the potential contribution of microgeneration in the UK (contrasted with solar thermal panels which, it said, were unlikely to be cost effective until around 2018).

But it is possible that this sudden vaulting into the centre of the UK energy strategy was the result of strong lobbying by some heavy players, with little justification to back it up.

In November 2005, the Carbon Trust published its first interim report from a large scale field trial of micro CHP. The results were lacklustre: about a third of the houses were saving carbon, a third were breaking even, and a third were actually emitting more carbon relative to the baseline. Needless to say, the industry was piqued.

Microgen’s reaction was to start looking for a buyer. According to Energy in Buildings and Industry (Feb 2007 – no link), British Gas and merchant bank Rothschilds spent this last year seeking a sale, but there were no takers. And now they’ve closed their doors, laying off 57 people.

In contrast Powergen, the other main player in the domestic CHP market, published its own interpretation of the raw data from the field trial and, using a different methodology, stated that in fact ALL of the test houses were saving carbon and saving money. A miraculous turnaround.

But they’d made some interesting assumptions. They used a much higher figure for carbon savings from each unit of electricity generated than the Carbon Trust (about 35% higher); they used their own boiler performance studies for the baseline; they built in a credit for exported electricity; and so on. There are justifications for their decisions, but it’s hard to take their report at face value given the source and the huge disparity between their results and those of the Carbon Trust’s first interim report.

So what’s next? The next interim report from the field trials will be published in April of this year and it’s unlikely to be as favourable as the Powergen response to the first report. Around the same time, the Carbon Trust will publish an agreed methodology for reporting on the performance of micro CHP engines, which should prevent drastic alternative interpretations of the data in the future.

The final report from the trial won’t be out until 2008 but we may not have to wait that long to see the effects of the findings. The fallout from the first interim report may have been enough to stop a major company in its tracks. An unfavourable second report could put the nail in the coffin of domestic-scale gas CHP.

I should note here that I’m a big supporter of CHP in general, but it works best on the medium and large scale (hotels, hospitals, city blocks) and not so well on small schemes where the demands are “peaky” and diversity is low.

The houses were a cross section. I agree with you about the limited applicability. Domestic scale CHP seems best suited to larger houses with higher heat demand (built before Part L 2002). So it’s really only for retrofit.

I think a lot of people knew this was the case but it was hard to be heard over all the hype from the industry.

One of the issues that still has to be addressed in the whole micro CHP debate is the integration with typical UK heating systems, also a new generation of advanced controls needs to be developed to optimise the operation of the micro CHP unit and it’s integrated condesing boiler. I suspect, based on advanced controls results from condensing boiler systems that if the right controls had been fitted to the test systems the results may have been more positive and the future for micro CHP brighter

Les, Thanks for the comment and I take your point. The first Carbon Trust interim report highlights the need to improve controls. But it seems to me that no amount of controls optimisation can adapt a gas micro CHP unit to the intermittent and peaky loads of a single house, especially given the long warm-up times required by the stirling engine (during which the units don’t generate electricity).

[…] Thursday, April 26th, 2007 in micro chp, chp, engineering, climate change, energy The people in charge of the micro-CHP field trial at the Carbon Trust say their next interim report will be delayed until early June with the calculation methodology to follow soon after. So we’ll have to wait a little longer for the verdict on micro-CHP. Interestingly, the MicroGen units are still in the trial so maybe it will become clearer why BG Microgen closed down. […]

It is now March,2010. We are no nearer to any long term economical energy solution,which the big energy suppliers are cunningly stopping. I cannot find the cost of any CHP anywhere on the Internet or plumping supplies. Do they want to sell them?? The feed in tariff should help but that is so complicated that few will be able to take advantage of it as the government cynically want. Why do we not see any chp’s in the plumbers merchants with the facts and price displayed. None of the plumping magazines publish costings,as they seem to be controlled be someone or something. I believe there has been so much invested in wasteful and inefficient products, the manufacturers have to keep making and selling them. It is well known that boilers can run off water and generate electric as well , but how do you tax water? The gas industry would collapse overnight,the electric supply and generation firms would lose billions££, the oil companies would lose billions, the heating oil suppliers would go bust, boiler manufacturers would have to change or go under. NO,I think the situation will change very little, and Britain would be ripped off for many years yet.